1. Field of Invention:
This invention relates generally to test probe assemblies for testing integrated circuit (IC) devices whose contact pads are deployed in a predetermined pattern in a common plane, and more particularly to an assembly of this type which includes a contactor formed of flexible film material having probe contacts formed on the undersurface thereof in a matching pattern, whereby when the IC device is caused to rise so that its contact pads engage the probe contacts, this action causes the probe contacts to scrub the contact pads to ensure effective electrical contact therewith.
2. Status of Prior Art:
Many circuits and complex multi-stage electronic systems previously regarded as economically unfeasible and impractical are now realizable in integrated circuit (IC) form. The fabrication of a single-crystal monolithic circuit involves the formation of diodes, transistors, resistors and capacitors on a single microelectronic substrate formed on a silicon wafer. The circuits are applied to the wafer by photolithography, each wafer containing an array of identical integrated sections. The wafer is then sliced into "dice," so that each die or chip carries a single integrated circuit.
In a typical IC chip, input and output terminals, power supply and other circuit terminals are created by metallized contact pads, usually deployed along the margins of the chip. The geometry of the chip is either square or rectangular, and the marginal locations of the contact pads thereon depend on the circuit configuration and the available marginal space.
In order to ensure that the various circuits in each IC chip are functioning properly, so that the chip will operate reliably in the electronic apparatus in which it is included, it is necessary to test the chip before it is installed. The packaging of an IC chip is relatively costly and time consuming, and because a significant number of IC chips fail the test and have to be discarded, it is also desirable that each chip be tested before being placed in its package.
An unpackaged IC chip which has no pins or leads can be electrically connected to IC chip testing instrumentation by means of a test probe card. One well known form of a test probe card is disclosed in the Evans U.S. Pat. No. 4,382,228. The card includes an opening providing access to the IC chip being tested, the opening being surrounded by a ring of spaced conductive platforms on which are anchored blade-like needle holders each having a deflectable needle extending therefrom to engage a respective contact pad on the IC chip being tested.
In a later Evans U.S. Pat. No. 4,719,417, the test probe card is provided with double-bent needles such that when the IC chip to be tested is raised upwardly to cause its contact pads to engage the tips of the needles, further upward movement of the chip gives rise to a lateral displacement of the tips along the surfaces of the contact pads. This displacement results in a scrubbing action which serves to remove any oxide film formed on the pads that would otherwise interfere with effective electrical contact.
As pointed out in the Evans U.S. Pat. No. 4,719,417, since all of the contact pads on the IC chip lie in a common plane and must be simultaneously engaged in order to carry out testing, it is essential that all needle tips or points lie in a plane parallel to the common plane of the IC chip. Consequently, a fundamental requirement of a needle type probe card is planarization of the needle points. The nature of conventional probe cards and the character of the assembly fixtures for setting up the probe positions for such cards are such that it is difficult to assemble probes with needle points lying exactly in the same plane.
Hence a test probe card for an IC device must have contact probes capable of carrying out a scrubbing action to remove oxide film from the contact pads of the device, and the contact probes must also lie in a common plane so that they all simultaneously engage the contact pads with the same degree of pressure. While these requirements are satisfied with a test probe card of the type shown in the Evans U. S. Pat. No. 4,719,417 in which the probes take the form of double-bent needles, a card of this type does not meet a requirement often encountered in IC chips now being produced which have a multitude of contact pads. With a high density of contact pads, it is as a practical matter impossible to crowd a corresponding number of needles on the test probe card without the needles touching each other, thereby rendering the card defective.
In order to provide a test probe card for IC chips having a high density of contact pads, the patent to Grangroth et al., U. S. Pat. No. 4,649,339, makes use of a flexible dielectric film having a sheet of copper laminated thereto that is etched to define conductive leads which terminate in probe contacts. These are patterned to mate with the contact pads of high density VLSI or other integrated circuits. To bring about engagement between the probe contacts on the flexible sheet and the contact pads on the IC chip, the flexible film is arranged as a diaphragm to cover an air chamber. When pressurized air is supplied to this chamber, the film is then flexed outwardly to conform to the surface of the IC chip.
The practical difficulty with this arrangement is that the bulging film fails to ensure planarization of the probe contacts thereon when they engage the IC contact pads. The absence of such planarization inhibits proper testing of the IC device.
A similar test probe arrangement suffering from the same disadvantage is disclosed in the Brown patent, U.S. Pat. No. 4,820,976, in which gas is supplied to a pressure chamber covered by a flexible film having probe contacts thereon which when the film is subjected to pneumatic pressure bulges outwardly to cause the probe contacts to engage the contact pads on an IC chip.
The Rath patent, U.S. Pat. No. 4,758,785, discloses a motorized lift system for raising an integrated circuit device upwardly against the probe contacts on a flexible film, above which is a resilient pressure pad of silicone rubber. The practical difficulty with this arrangement is that the rubber pressure pad does not ensure planarization of the probe contacts, and without such planarization, proper testing cannot be effected.
It must be borne in mind that an IC wafer whose contact pads lie in a common plane, when raised by a lifting mechanism toward a probe test card in which the probe contacts are formed on a flexible film may be caused to assume a slight angle relative to the plane of the film. As a consequence, the contact pressure between the probe contacts and the contact pads will not be uniform, and this may militate against effective testing of the device.